1. Field of the Invention
This invention relates generally to high voltage electrical cables used to connect an electrostatic spray coating gun to a high voltage power supply, and more particularly relates to a high voltage cable wherein the conductive path of the cable includes distributed solid resistors.
2. Description of the Prior Art
High voltage electrical cables comprising distributed solid resistors throughout the cable length have been known in both the automotive industry for spark plug cables, and in the electrostatic spray coating industry for high voltage electrical power cables. In the electrostatic spray coating industry such cables have been used for several years. For a discussion of the benefits of such cables to the Electrostatic Spray Coating Industry, reference can be made to U.S. Pat. No. 3,348,186 issued to S. R. Rosen and assigned to the assignee of the present invention. However, prior art cables such as this did exhibit drawbacks for which it is an object of this invention to overcome.
The prior art devices used in the Electrostatic Spray Coating Industry almost invariably used short (approximately 0.25 inches) carbon composition resistors connected by means of a short conductive link, with the whole assembly being sheathed along its length by a dielectric, such as polyethylene, of an appreciable thickness. Additional layers of other coverings were also used. For a discussion of the purposes of these additional coverings, reference can again be made to the above mentioned Rosen patent.
The carbon composition resistors were brittle, and therefore if the cable were stepped on or run over with a truck or the like they would fracture and hence could cause failure of the cable. Further, because there were so many resistors in such close proximity to each other, the cable itself was very stiff and bulky.
The dielectric sheathing might be considered flexible by some standards, but stiff by others. That is, it will bend, but if it has any appreciable radial thickness it would no be considered limp.
In normal use of these prior art cables it would not be uncommon for the cable to be looped randomly on the floor. Further, in normal use of these cables, it would not be uncommon for the cable to be pulled from an end with one of these loops still in the cable. If this happened, and there were no forces causing the loop to untwist, the loop would be pulled smaller as the pulling force increased. In the prior art cables one of the short brittle resistors might remain in the center or midpoint of the pulled loop where mechanical stresses resulting in the cable are greatest, resulting in fracture of the resistor. Even if the resistor were strong enough to withstand the mechanical stresses applied to it in midpoint of a pulled loop, severe deforming stresses could result in the polyethylene sheath which could adversely affect its insulating ability.